The production of vulcanized rubber items based on hydrogenated nitrile rubbers is known in particular for drive belts, roll coverings, gaskets, hoses and cables. If the items based on partially hydrogenated nitrile rubbers are produced via sulphur vulcanization according to DE-A-29 139 92 or EP-A-0 265 706, the properties of these rubber items then become inadequate in particular at the high temperatures nowadays encountered in various applications. Vulcanisates with better ageing resistance are obtained on the basis of more highly hydrogenated nitrile rubbers which are vulcanized with sulphur according to EP-A-0 112 109, or with the aid of organic peroxides according to DE-A-34 38 414, or else with inorganic peroxides according to EP-A-0 383 127. However, the hardness and also the tensile stress values at various tensile strain values can still be improved, both at room temperature and at higher temperatures, for example at 130° C. Additions of salts of unsaturated carboxylic acids is a successful method in the case of peroxidically vulcanized nitrile rubbers for improving hardness and the level of modulus, both at room temperature and at 130° C. The salts of the unsaturated carboxylic acids here can be prepared “in situ” (U.S. Pat. No. 5,391,627) during preparation of the compounded material from the oxides and the corresponding unsaturated carboxylic acids. However, according to U.S. Pat. No. 5,208,294 it is also possible to add the salts of the unsaturated carboxylic acids directly. In this case, the salts of the unsaturated carboxylic acids are prepared in a separate step of a process or are purchased.
However, with the aim of further improvement in the property profile of vulcanized rubber items based on hydrogenated nitrile rubbers, in particular for use in drive belts, in rolls, in gaskets, in hoses and in cables, a further improvement in mechanical properties is desirable and specifically also at high temperatures of 130° C. or above, these being temperatures that can particularly and increasingly arise in automobile applications. The intention is that this improved property profile is to be retained even over a prolonged period of storage at these temperatures. However, at the same time the intention is that rubber items improved in this way have unaltered good hardness values.
The use of rubber gels, also termed microgels, is known for underlying control of the properties of vulcanisates (e.g. EP-A-0 405 216, DE-A 42 20 563, GB Patent 1078400, DE-A-197 01 487, DE-A-197 01 489, DE-A-197 01 488, DE-A-198 34 804, DE-A-198 34 803, DE-A-198 34 802, EP-A-1 063 259, DE-A-199 39 865, DE-A-199 42 620, DE-A-199 42 614, DE-A-100 21 070, DE-A-100 38 488, DE-A-100 39 749, DE-A-100 52 287, DE-A-100 56 311 and DE-A-100 61 174). These specifications disclose improvement of various vulcanisate properties via additions of microgels, but not with the focus on high-temperature applications.